Shoulder Armor is armor used by Tapio in his Matoran Nuva form. He can activate the shoulder armor anytime he wants, but he usually doesn't use them, since they are very heavy. The armor is just two protodermis shields on his soulders.

Tapio actually got his shoulder armor when he became a Mega Matoran. He didn't have the ability to unactivate them by then, however. That skill came with the transformation into a Matoran Nuva.